USGS photoDeepwater ciscoes can grow up to a foot long. The ones being stocked, though, are about half that size.

It’s all about giving the big fish in Lake Ontario something else to feed on, and in the process increasing the success rate of their spawning.

That’s the reasoning behind a stocking effort that began this past week of stocking deepwater cisco, a baitfish, offshore from Oswego. It’s the result of a collaborative effort between state, federal and Canadian agencies.

Deepwater cisco haven’t been seen in Lake Ontario in nearly 30 years. The last known fish was collected in 1983. This stocking program is a first in the Great Lakes.

The baitfish grow up to 10-12 inches. They feed primarily on plankton and invertebrates in water depths from 180 feet to 650 feet. They once were an important food source for native lake trout, Atlantic salmon and burbot in Lake Ontario, said Jim Johnson, lab director for the USGS Tunison Laboratory of Aquatic Science in Cortland.

By the mid-20th century, though, populations took a nose dive because of over-harvesting by anglers, along with competition from populations of invasive alewife and rainbow smelt.

The downside of the deepwater cisco’s disappearance has been that lake trout and salmon that feed primarily on alewife can experience reproductive failure due to a vitamin B deficiency, caused by the chemical thiamanase in that baitfish. Fish that feed on native species like deepwater cisco, though, are less likely to experience problems with their eggs and fry, Johnson said.

Chinook and coho salmon currently being raised at the state Department of Environmental Conservation hatchery in Altmar often have a B-1 deficiency and have to be bathed in Vitamin B-1 solution, he said.

USGS photoDeepwater cisco in a fish tank at the USGS Tunison Lab in Cortland.

The new deepwater cisco stocking program is a cooperative, effort between the DEC, the Ontario Ministry of Natural Resources, the U.S. Fish and Wildlife Service, the U.S. Geological Survey and the Great Lakes Fishery Commission.

The juvenile fish (about 5 inches long) stocked this past week originated from eggs collected by the United States Fish and Wildlife Service staff on Lake Michigan during January and February of this year. Eggs were hatched and juveniles reared at the Tunison Lab in Cortland, and the White Lake Fish Culture Station run by Ontario Ministry of Natural Resources.

This year, a total of 21,000 will be stocked and the effort is expected to be long term, Johnson said.

"This is unique. There’s nobody anywhere in the world, at any time, that’s tried to restore a forage species in a lake the size of Lake Ontario in order to restore the resilience of the native fish community," Johnson said. "If this is successful, it will make it more difficult for other invasive species to get a foothold on this part of the lake."